1. Field of the Invention
The present invention relates to a process for removing peroxides from peroxide containing aqueous waste streams such as those from the propylene oxide/styrene monomer technology so that the treated stream can be further processed prior to its disposal.
2. Description of the Prior Art
The Oxirane process for the production of propylene oxide and styrene monomer is a process of very great commercial importance. The basic patent describing this process is U.S. Pat. No. 3,351,635. In the process, ethylbenzene is oxidized to ethylbenzene hydroperoxide, the ethylbenzene hydroperoxide is catalytically reacted with propylene to form propylene oxide and 1-phenyl ethanol, and the 1-phenyl ethanol is dehydrated to form styrene monomer.
In practice of the process there are a number of separation and recovery steps and various purge streams are formed which must be disposed of in the face of ever increasing environmental concerns. In various instances, disposal practices which were permitted in the past may, in the future, no longer be permitted. Accordingly, considerable efforts are being directed to bring about improvements in procedures used to treat propylene oxide/styrene monomer purge streams.
One such purge stream is an acidic wastewater removed as a distillation sidestream. The acidic wastewater contains in addition to water and various organic acids, significant amounts of ethylbenzene and peroxidic materials. Consideration has been given to biotreatment of such streams but the contained ethylbenzene tends to flash in a biopond exceeding VOC limits. First stripping ethylbenzene before biotreatment is an option but this would result in dangerous concentrations of peroxides forming within the stripper.
Chemical treatment such as with caustic to decompose the peroxides is an option. However, such treatment is costly and yields a salty stream that is more difficult to biotreat. Chemical treatment as with homogeneous catalysts is possible but is more costly due to chemical usage and mixing and metering equipment. The chemicals added may also result in environmental issues downstream especially if it is necessary to increase the pH.
Decomposition of peroxides in acidic environments is possible via heterogeneous catalysis. Certain activated carbons, for example, have been demonstrated to work. However, such systems are known to have plugging problems because the evolved oxygen bubbles attach to the fines and promote their agglomeration. Also, the carbon tends to adsorb other organics in the stream and deactivate over time. Lastly, oxidation of the carbon itself might occur in "hot spots" throughout the catalyst bed, or even local combustion of carbon.